1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copying apparatus or a facsimile, and more particularly to an image forming apparatus utilizing an intermediate transferring member.
2. Related Background Art
As an image forming apparatus of electrophotographic process, there is already commercialized a multi-color image forming apparatus of transferring a developer image (toner image), formed on a first image bearing member such as single or plural photosensitive drums, onto an intermediate transferring member constituting a second image bearing member thereby forming a toner image of plural colors on the intermediate transferring member, and transferring the toner image of the plural colors on the intermediate transferring member onto a transfer material constituting a third image bearing member thereby forming a multi-color image.
In such known multi-color image forming apparatus, the intermediate transferring member is in contact, at a primary transfer portion, with the photosensitive drum, and a toner image formed on the photosensitive drum is once transferred (primary transfer) onto the intermediate transferring member, and is then transferred (secondary transfer), at a secondary transfer portion, from the intermediate transferring member onto the transfer material. Thereafter the transfer material, bearing the transferred toner image, arrives at a fixing apparatus and is subjected to heat and pressure therein to obtain a permanently fixed image. On the other hand, toner remaining on the intermediate transferring member after the secondary transfer is cleaned from the intermediate transferring member.
In the above-described multi-color image forming apparatus of intermediate transferring type, there is obtained an advantage that limitation is reduced in conveying the transfer material, since the toner images formed on the intermediate transferring member are collectively transferred to the transfer material.
On the other hand, since the transfer is executed plural times such as the primary transfer and the secondary transfer, there is encountered a drawback that the density becomes extremely low unless a transfer efficiency is improved, for example, by employing toner with an excellent transfer efficiency. Also there is encountered a drawback that a transferring property fluctuates in time or locally, thereby resulting in an instability of the image quality, unless a surface of the intermediate transferring member, bearing the toner image, is uniform and stable in time.